This invention generally relates to electronic memories, and more particularly, the invention relates to refreshing memory cells of a phase change material memory device.
A phase change material may be used to store the memory state of a memory cell of a semiconductor memory device. In this manner, phase change materials that are used in phase change material memory devices may exhibit at least two different states. The states may be called the amorphous and crystalline states. Transitions between these states may be selectively initiated. The states may be distinguished because the amorphous state generally exhibits higher resistivity than the crystalline state. The amorphous state involves a more disordered atomic structure. Generally any phase change material may be utilized to exhibit these two states. However, as an example, thin-film chalcogenide alloy materials may be particularly suitable.
The phase change may be induced reversibly. Therefore, the phase change material may change from the amorphous to the crystalline state and may revert back to the amorphous state thereafter, or vice versa, in response to temperature changes. In effect, when the phase change material is used in a memory cell, the memory cell may be thought of as a programmable resistor, which reversibly changes between higher and lower resistance states. The phase change may be induced by resistive heating that is caused by a current that flows through the material.